Method and apparatus for rolling screws



March 23, 1943.

METHOD AND APP Filed Aug. 1,7, 1939 253145390 A ARATUs FR ROLLING scfmwsl '7 Sheets-Sheet 1 g um Q EM @am ma@ I l M7/Wy W.y A. DE VELLIER '7Sheets-Sheet 2 www/HMH @Mq-M' w. A. DE VELLIER 2,314,390

' METHOD AND ARPARATUS FQR ROLLING SCREWS vlvlalrcl. 23, 1943.

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March 23,. 1943. w` A DEjVE'l- UER 2,314,39

METHOD AND'APPARATUS FOR ROLLING SCREWS Filed Aug. 17, 1939 '7Sheets-sheen;

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March 23', 1943. w. A. DE vl-:LLIER METHOD AND APPARATUS FOR ROLLINGSCREWS Filed Aug. 17, 1939 7 Sheets-Sheet 5 METHOD AND APPARATUS FORROLLING SCREWS` Filed VAug. 1'7, 1939 '7 Shee*{'.S-Sheeb4 6 March 2,3,1943. w. A. DE VELLIER METHOD AND APPARATUS FOR ROLLING SCREWS frsheeis-sneex 7 Filed Aug. *17,I 1939 'the fact larly when making thePatented Mar. 23,"1943 I ltlETHOD AND APPARATUS FOR ROLLIN SCREWSNewark, N; J., assignor to Corporation, Waterville, Conn., a corporationof Delaware implication August 17, 1939, serial No. 290,621 (ci. sil- 9)`uriuiam A. De Venier,

New Process Screw S Claims.

My invention relates to improvements in methods of manufacture of screwsand includes, in addition, novel types of apparatus for carrying -outsaid methods. While my invention is particularly adapted for use inproducing the double thread single point screw, shown in Arenz PatentNo.- 1,912,879, it is obvious that I may'alsoemploy -it in themanufacture of other types of screws, whether employinga singleormultiple thread. A

My invention particularly relates to the precision manufacture of screwsin which the manufacturing machines are so designed as to use up all themetal and thereby produce no waste.` In the usual manufacture of screwsby cutting threads thereon, at least 33% of the metal is cut away andwasted.' With my inproved-precision method of rolling, as heretoforestated, no waste at all is produced.

Further features of my invention relates to` the speed at which it ispossible to manufacture screws employing my improved method, permittingone toroll ten timesas many screws' as it was possible to make in theprior art by cutting methods.

A further feature of my invention resides in the fact that inasmuch asthe machines employed are precision machines, absolute uniformity in thefinished product results.

A further object of my invention is to provide screws having moreinherent strength than otherwise heretoforeproduced.

vention from a wire of smaller size than employed a wire of .216" .242"diameter to make a #14 screw, thereby additionallyeffecting aconsiderable saving in the cost of the wire.

Further features of my invention relate to improvements in the blankextrusion method and A further feature of my invention resides in thatemploying my improved rolling method I am able to provide each threadwith a sharp razor-like cutting edge.

An additional feature of-my invention resides in the fact that I do n otdisturb the portion of the screw blank to be rolled by any type ofextrusion, thus leaving the actual rolling operation as the only shapingoperation performed on this portion of the screw blank, to give it moreinherent strength and to eliminate the scale which is sometimes presenton metal that has been overworked.

A further feature of my invention, particutypeof screw shown in saidArenz patent, is to provide a screw having suiilclent metal at the tipthereof to form a sharp dlametric cutting edge, thus providing aninelsing blade projecting axially forwardly from each opposite.` sidewall of the `pointed portion thereof.

A further feature cf the fact that I am able my invention resides in tomanufacture my inapparatus, and also improvements in the rolling methodand apparatus.

ther features vof my invention reside in improvements in the novel ltypeof screws produced thereby.

These and such other objects of my invention as may hereinafter appearmay be best understood from a description of embodiments thereof such asare shown in the accompanying draw-` ings. 1

In the drawings, Figs. 1-4 are diagrammatic sectional views illustratingthe steps in the method I preferably employ to form a screw blank, Fig..l illustrating the initial step of feeding the wire through a hole inthe base and an aligned axial hole in the die to a. predetermined pointabove said die, Fig. 2 illustrating the relative lateralmovement betweenthe dieand base tocut off said wire to leave the lower end of said pieceof wire resting on said base and to move the piece of wire directlyunderneath the punch', Fig. 3 illustrating the application of the firstpunching blow to the piece of wire to shape the tapered and bodyportions of the blank to the desired shape, yand Fig. 4 illustrating theapplication of the second punching blow to cause the metal to flowobllquely and radially outwardly to die yand punch, with the wire fedthrough the hole in the base and aligned: axial hole in the' die to thedesired predetermined height.

Fig. 'l is a perspective view of the parts shown in Fig. 6 after the diehas been relatively moved over the base to cut the wire to apredetermined length and to bring it in position immediately below thepunch. Y

Figs. 8-12 illustrate 'additional steps in the method of making oneembodiment of screw produced by my invention, namely a double-threadedscrew of the Arenz type having a widely domed pointu to providesuiiicient metal therein for its diametrlc cutting blades, Fig.- 8 beinga diagrammatic view illustrating the step of obliquely reformerly,specifically being able to employdiameter as against a wire of 1 Fig. 32is an end elevation of the stationary die 80.

In the drawings, wherein like characters of reference indicate likeparts throughout, 40 generally indicates a rolled thread screwconstructed in accordance with my'inventon.

two suitably shaped dies, Fig. 11 being an enlarged diagrammaticsectional view of the tip of the pointed portion of the rolled screw andadjacent portions of the dies shown in Fig. and Fig. 12 being a sideelevati'on of the completely rolled single point double threaded screwproduced by my invention.

Figs. 13-17 illustrate additional steps in the method of making anotherembodiment of screw, namely a double threaded screw of the Arenz typehaving a sharper point, Fig. 13` beingv a diagrammatic view illustratingthe step of obliquely removing metal from the lower end of said blank toprovide a conical point, Fig. 1.4 being a side elevation of the thuspointed screw blank, Fig. 15 I being a diagrammatic sectional viewillustrating the step of rolling the threads between two suitably shapeddies, Fig. 16 being an enlarged diagrammatic sectional view of the tipof the pointed portion of the rolled screw and adjacent portions of thedie shown in Fig. 15 and Fig. 1'1 being a side elevation of such acompletely rolled double threaded screw produced by my invention.

Figs. 18-22 illustrate additional steps in the method of making anotherembodiment of screw, namely a single threaded more sharply pointedscrew, Fig. 18 being a diagrammatic view illustrating the step ofobliquely removing metal from the lower end of said blank to provide aconical point, Fig. 19 being a side elevation of the thus pointed screwblank, Fig. 20 being a diagrammatic sectional View illustrating the stepof rollingthe threads between two suitably shaped dies; Fig. 21 being anenlarged diagrammatic sectional view of the tip of the pointed portionof the rolled'screw and adjacent portions of the diesshown in Fig. 20

and Fig. 22 being a side elevation of such a completely rolled threadedscrew produced bymy invention.

Fig. 23 is an enlarged fragmentary plan view of As illustrated in Figs.l-7, my improved method includes the steps ofstrikingan end of a conlnedpiece of wire 42 of such greater length than the finished blank 44 toprovide the desired amount of metal in said finished blank with suchforce as to cause the metal in the upper portion of said piece of wireto ilow axially and radially to form the upper portion of said piece 42into a blank body portion 46 of greater circumference than that of theoriginal piece of Wire 42, with an outwardly tapered head 48 above saidcircumferentially expanded body portion and an inwardly tapered portion50 below said expanded body portion while confining the lower end 15 ofsaid piece o f wire 42 and lower portion 52 thereof below saidinwardly'tapered portion 50 to a lower shank portion 52 having theoriginal circumference of said wire. I then suitably point the lower endof said screw blank 44 to provide a suitable pointed portion 54. I thenroll threads through the tapered, shank and pointed portions 50, 52 and544 respectively, as illustrated in Figs. 8-28 and Figs. 30,-32, byapplyingradial inward pressure at equally spaced lanes extendingspirally of said portions to force the metal radially inwardly to formequally spaced spiral lands 56 and permitting th'e displaced metal to owradially outwardly between said spiral lanes of pressure while thethread rolling apparatus I preferably employ showing the dies and ascrew blank in position lto .be rolled.

Fig. 24 isa view of the thread forming'faces of the companion dies whichroll the threads on the screw blank.

Figs. 25-27 illustrate my improved method of forming these dies, Fig. 25being an end elevation of' a die blank, Fig. 26 being a view similar toFig. 25 after a portion of said die'adjacent o ne edge thereof has beenremoved, and Fig. 27 being a view similar to Fig. 26 after the blankreceiving cavity and threads have been out thereon.

Fig. 28 is a diagrammatic sectional view of the dies showing the screwbeing rolled therebetween.

of the thread rolling dies about to engage the screw blank at thebeginning of thelrstr'oke and illustrating the fact that the lower wallsof the cavity are slightly inclined upwardly from front Vto rear. I

Fig. 31 is a plan view similar to Fig. 30 illustrating the dies at theend of their stroke after they have rolled a screw from the blank shown'in conning said radial outward flow to sharp equally spaced ridge meansof/substantially the circumference of said blank body portion .46 toprovide continuous spiral thread means 58 tapering to a sharp cuttingedge 60 of substantially the circumference of said blank body portion 46extending spirally downwardly through saidl portions of progressivelyincreasing vheight in said tapered portion 5U, of substantially equalheight throughout said shankportion 52 and of progressively decreasing height in said pointed portion 54 and terminating in a cutting edge 62'atthe tip thereof, the inwardv radial pressure being predetermined itoextrude the metal radially inwardly in said. pressurelanes` in an amountsuillcient only to' extrude sullicient metal radially' outwardly to formsaid threads.

While the various steps -of my improved meththe desiredamount of metalin the formed blank A 44. Said axial die hole 58 has a blank shankforming portion 52a at the lower end thereof of substantially thecircumference of said piece of wire 42,'an outwardly upwardly taperedvportion 50a above said shankfo'rming portion 52a, a

blank body forming portion 48aof greater circumference above saidtapered portion 50a and' I an outwardly and more sharply taperedheadblank forming portion 48a terminating substantially flush with theupper end of said die 1l.

As shown in Figs. 6 and 7, the extrusion punch preferably includes threeparts, namely the base El, the die 'I0 and the punch 14. Means areprovided torelatively laterally move said die 'I4 re1- -ing at thisangle V said die.

excess of metal thereon forming cavity 48a and they head forming cavityative to said base 68 to cut off a piece 4240i said wire 4I to leave thelower end 15 of said piece of wire 42 resting on said base 56 andbringing the hole 68 containing the piece of wire 42 in augment with thepunch 14. Ilhave found that best results can be obtained by providing a.taper in the tapered portion 58 of said blankrv or 58a of said die ofbetween 1826, the metal extrudwithout any cleavage or fracture orappreciable weakening' of its crystalline structure. r I then, bysuitable sharp lowering of the punch 14, apply a punching blow-to theupper end 12 of said piece of wire 42, as illustrated in Fig. 3 (thelower end 15 of said piece of wire 42 resting against said base 66), toshorten the wire axially and to causeit to iiow obliquely and radiallyoutwardly to iill up the tapered portion' 58a of said die hole 58 toform the tapered portion of said blank and also to fill up said blankbody portion 45a of said die to form the body portion 46 of said ter. Ithen as shown in punching blow of ened upper end of said wire to furthershorten said wire axially and to cause the balance'of the wire stockabove said die 10 to flow obliquely and radially outwardly to fill upthe more sharply tapered head blank forming portion 48a of said die toform the head 48 in said blank 44. The screw blank may be then suitablyremoved from Fig. 4, 'apply' a second I then suitably point the lower`end of said 'screw blank to provide it with a pointed portion' 54terminating in a point 16. While this may be done in a suitableextrusion pointing machine or in any other suitable manner, in' thepreferred embodiment shown, I preferably form the pointed portion 54 byobliquely removing metal from the lower end of said blank to form saidconical pointed portion 54. If I desire to make a double threaded screwof the type heretofore referred to, the blank is preferably providedwith a 40 cone and with 'the side wall 18 ofv said conical portion 54supplementally outwardly domed 3 to 5 more. It is obvious that in thisstage of its manufacture, my improved screw blank adapted 48a withoutproviding anyexcess metal.

As stated, two additional features of my invention relate to in saidArenz patent, the diame- 52 of said threads adjacent -the point 16 andthe point -'i6 itself are formed by an axial extrusion, the dies h8 and9 shown in said patentbeing separated for this purpose. 4

Employing my improved method, however, I keep the facesof thecooperating dies in contacting 20 blank of relatively larger diamethepunch 14 to the then shortrolled onthe tapered portion 58, the shank Iof said respective portions to'have screw threads rolled thereoncomprises a piece of wire having a pointed lower portion 54, a shankportion 52 of uniform circumference above said pointed portion 54, anoutwardly upfwardly tapered portion above said shank portion, anexpanded `sired resistance formed therein, whether it comprisesy theusual slot for receiving the end of a flat screwdriver, a truncateddiamond as shown in my Patent No. 2,218,701, or a Phillips recess orother type of slot. If desired, the wail 18 of the conical point 16 maybe providdwith an greater than required for a conical point of anysuitable shape in any suitable manner and f or this purpose may besupplementally outwardly. domed, and I preferably employ a conicalpointed portion of between 30 to 40, if I desire to roll the doublethreads of the type shown in saidvArenz patent and to provide thedesired diametric cuttingbiai'lesv 62 thereon. It will be apparent thatevery step in the forming operation is exactly extruded outwardly to llthe respective tapered portionforming cavity 50a, the ybody l spaceddistances throughout predetermined, the piece of wire 42 being cut of!at such a length as to be vedge'li2 of the other thread 58, eachtapering '.blank 44 between the faces spective corresponding blankportions -pointed portions increasing depth in said tapered engagementat all times, thereby substantially eliminating any axial extrusion andlimiting the extrusion to radial inwards and radial outwards extrusion,said radial extrusion tapering oil obliquely in said pointed portion 54as the point 16 of the screw is reached. The threads 58- are 52 andpointed portion 54 of said blank only, and

die 8'8, while confining the tapered, shank and pointed portions 58, 52and 54 respectively of said 82 and 84 of said respective dies, 'eachrespective face 82 and 84 of said respective dies comprising acontinuous cavity having a cooperating inwardly tapered portion 50hadjacent an edge thereof, a cooperating shank-forming portion 52h and apointed portion 54h tapering outwardly to the surface 88 of saidrespective die beyond saidcavity 85 substantially abutting the oppositedie surface, all 58h, 52h and 54h being ofthe re- 50, 52 and 54 toextrude metal from said blank radially inwardly to formcontinuous spacedlands 56 in said portions, each respective face 82 and 84 having equallyspaced continuous thread forming groove means 58h therein, eachterminating in a sharp inner intaglio liquely inwardly thereof to adepth substantially that of the radius of the blank body portion, fromthe outer surface of less respective depth than the radii the height ofsaid respective face through said tapered, shank and 50h, 52h and 54hrespectively of progressively portion 50h, shank portion substantiallyequal depth in said 52h and of progressively decreasing depth in saidpointed portion 5417 to receive the metal extruded radially outwardly bysaid lanes of pressure andconiine it to form continuous threads sharpspiral cutting edge 5U of substantiallyv the circumference of said bodyportion 46 in said tapered, shank and pointed portions 58,- 52 and 54and of progressivelyy increasing height in said tapered portion 50 dueto the taper of said portion, even height through said shank portion 52and progressively decreasing height in said pointed portion 54. If therespective grooves 58h are of a shape and number to provide a doublethread of the Arenz type, it is obvious that the respective two doublethreads 58 will each terminate ina respective cutting edge 62 at the tipthereof in diametric relationship ,to the cutting downwardly to a vpointcoincident with the point improvements in the method of and apparatusfor rolling threads on my improved It will be noted, however, that inthe l ridge 60D, extending ob- 88 of said die at equally l,

58, each tapering outwardly to a- 18 of said screw stem as shown inFigs. 8-22. It will be observed that the two respective dies 18 and 80are of unitary construction throughout, thereby. eliminating all errorsin matching up parts, l as found objectionable in the. Arena type die.It will be also noted that a similar precision method of rolling takesplace, the `surface of the The lanes Sib andthe grooves :58h areprefer-l ably as in the embodiment shown of substantially equal widththroughout their length and the lands 56h are preferably inclinedslightly upwardly as shown in Figs. 30-32 from the front to the rear ofeach die to provide the predetermined progressively increasingradialpressure heretofore referred to while the faces 88 of -each dieare maintained in contact at all times to prevent axial extrusion at thetip. It is obvious that with this construction the equally spaced lanesof equal width in each die will come progressively y closer to eachother to progressively compress said equally spaced lands on the screwand progressively force a larger amount of metal into said equallyspaced grooves of equal, depth and width as the screw is rolled.

Figs. 25-27 illustrate amethod of making such a die, which comprisesobliquely removing a porsharper point 54' maybe desirable-for somereasons, it does not provide quite as good cutting blades 62' at the tip16 as the 40 cone shownin the embodiment shown in Figs. 8-12..

I have also shown in Figs. 18-'22 my invention employed in Aa singlethread screw 40" terminating in a single `cutting edge 62" which may beequally successfully rolled by my invention. In rolling a doublethreaded screw the pointed portion preferably comprises a cone having apoint Aof between 30.-40, preferably nearer 40, and

the double threads 58 or 58' having a. pitch angle of between '7l/2 to121/2", in the embodiments shown in Figs. 8-17 having a pitch angle ofapproximately 10. In the single thread embodiment shown in Figs. 18-22,however I preferably employ a pointed portion 54" comprising a 15-25cone,.in the embodiment shown vin the drawings, a 20 cone and the singlethread 58" employed therein hasla pitch angle of Vbetween 48, in theembodiment shown in the drawings exactly 5. It is obvious, however, thatmy improved method is equally applicable in rolling any typel of singleor multiple thread type of in a vertical plane, it is obvious that thescrews may be rolled in a horizontal or any other plane withoutdeparting from my invention.

It is apparent, therefore, that I have provided t a novel process ofmaking a complete screw by tion of said die adjacent one edge thereof bycutting or otherwise to form the tapered wall 50h and then concaving theface of. the die with a screw blank concavity 86 of the desiredv shapeand suitably forming the thread forming grooves lib in said cavity,preferably by a suitable hob whereby the thread forming grooves are ofprogressively less respective depth in the tapered portion 50 of thescrew blank opposite said tapered die wall 50h. It will be noted thatthe top die 18 is mounted in `its respective machine part so as to havethe face 88 thereof contactingly engage the cooperating face 08 of the stationary die 80 in use.

I have shown in the drawings three different embodiments of screws whichmay be rolled by my invention, Figs. 8-12 illustrating a double threadsingle point screw of the Arenz type terminating in tapered or pointeddiametric cutting edges B2 at the tip 16 thereof. In all embodiments inmy invention 'it will be noted that.

there is substantially no axial extrusion, the amount of metal extrudedradially outwardly exactly matching the amount of metal extrudedradially inwardly to provide enough metal for the cutting threads. Asstated, I preferably provide a pointed portion comprising a cone asshown in Figs. 8-12. In addition, as stated, the Wall 18 of said pointis preferably supplementally outwardly domed or curved with a 35 curveso as to aid insproviding suillcient metal for the diametric cuttingblades 62 at the tip 16 of the pointed portion 54, the cutting surface90 of the cutting tool 92 being suitably concaved to produce thisprecision extrusion and precision rolling, that I Ahave provided novelfeatures in the method and apparatus for forming a -blank and novelfeatures in the apparatus and method for rolling the threads, a noveltype of screw blank and various nove1 species of completed screws soproduced by my method and apparatus with the advantages described above.It will be observed-that inasmuch as the circumference of the threads issubstantially the same as the circumference of the body portion, thescrews may be readily inserted *without diiliculty, and will form alvbiting grip when so inserted.

It is understood that my invention is not limited to the specificembodiments shown or methods or apparatus described `and that variousdeviations may be made therefrom without departing from the spirit andscope of the appended claims.

What I claimis:

1. The rmethod of rolling threads on the shank and pointedportions of ascrew blank having a. v pointed end portion having anl excess of metalthereon greater than required for a conical point and ,a shank portionabove said pointed end, which comprises rolling threads in the shank andpointed portion/s) of said blank by applying progressively increasingradial inward pressure at equally spaced flat lanes of equal widthextending spirallyof said portions to force the metal radially inwardlyto form spaced spiral lands of equal width and permitting the displacedmetal to iiow radially outwardlyl between said spiral lanes of pressurewhile confining said radial outward ow of metal to sharp continuousequally spaced ridge means of equal width while positivelyl inhibitingany axial extrusion at the tip of said pointed end to provide twocontinuous equally spaced thread means of even width each taperingyto asharp cutting edge extending spirally downwardly throughout saidportions, of substanand of progressively decreasing height in said ,ingoutwardly a,s14,soo

pointed portion and terminatingin a downwardly tapered diametric cuttingedge' at the tip thereof, the inward radial pressure being predeterminedto extrude the metal radially inwardly in said pressurelanes in anamount suihcient to extrude suilicient metal radially outwardly to formsaid threads.

2.- The method ofl rolling threads on the shank and pointed portions ofa screw blank having a ypointed end portion and 'a shank portion abovesaid pointed end,which comprises rolling. threads -in the shank andpointed portions of said blank by applying progressively increasingradial inward pressure at equally spaced flat lanes of substantiallyequal width extending spirally of said portions to force i: metalradially inwardly to form 'spaced spiral width and permitting thedisplaced metal to flow radially outwardly between said spiral lanes ofpressure while confining said radial outward flow of metal to sharpcontinuous equally spaced ridge means of equal width while positivelyinhibiting. any axial extrusion at the tip of said pointed end toprovide continuous equally spaced threadmeans tapering to a sharpcutting edge extending spirally downwardly throughout said portions, ofsubstantially l shank portion and o f progressively decreasing heightAin said pointed portion 'and terminating in a cutting edge at the tipthereof, the inward radial pressure being predetermined -to extrude themetal radially inwardly in said pressure lanes in an amount sulcient toextrude suillcient meta radially outwardly -to form said threads. v

3. Apparatus for use in rolling threads on screw blanks having a pointedlower end portion having an excess of metal thereon greater thanrequired for a conical point and a shank portion of uniformcircumference above said pointed endportion, comprising a stationarydie, a movable die, means to move Ysaid movable die over said stationarydie in contacting engagement therewith, each' die having a facecomprising a continuous cavity having a lower wall inclined slightlyupwardly from. front to rear having a cooperatingv substantiallyflatshank forming portion and a point forming portion tapering outwardlyto the surface of vsaid die beyondsaid cavity substantially abutting thebpposite die surface, all such portions being of less respective depththan the radii of the corresponding blank portions to progressivelyextrude. metal from said blank radially inwardly to form continuousequally spaced lands equal height throughout said` ands of substantiallyequal t of substantially equal depth y throughout said shank portion andscrew blank having a pointed lower end lportion vand a shank portion ofuniform circumference above said pointed end portion, comprising astationaryl die, a movable die, means to ,move said movable die oversaid stationary die lin contacting engagement. therewith, each diehaving 'a face comprising Ma continuous cavity having a lower wallinclined slightly upwardly from front to rear having a cooperatingsubstantially ilat shank forming portion and a pint forming portiontapering outwardly to the surface'ofrsaid die beyond said cavitysubstantially abutting the opposite die surface, all such portions beingof less respective depth than the radii responding blank portions toprogressively extrude metal from said. blank radially inwardly to formcontinuous equally spaced lands of equall width in said portions, eachface'having continuous equally spaced thread forming groove means ofsubstantially uniform width throughout the length thereof eachterminating in a sharp lntaglio ridge-extending obllquely inwardlythereof to a predetermined depth at substantially equally spaceddistances throughout the height of said face through said shank andpointed portions, y in sai-d shank portion and of progressivelydecreasing depth in said pointed portion, to receive the metalprogressiyely extruded radially outwardly by said inclined lanes ofpressure between said grooves and confine it to form continuous threadmeans o'f even width tapering outwardly to a sharp continuous spiralcutting edge of even height decreasing height in said pointed portionv.and terminating in a cutting edge at the tip thereof.

5. A pair of relatively'movable one piece screw thread rolling dieshaving opposing surfaces adapted to contact each other in use, eachhaving a face comprising. a continuous cavity hav-- ing a lower Iwallinclined slightly upwardly from front to rear having a cooperatingsubstantially flat shank forming portion and a point forming portiontapering outwardly to the surface of said die beyond said cavity, eachface having continuous equally spacedthread forming groove means each ofsubstantially uniform width throughout its length and terminating in asharp intaglio thereof rid-ge extending obliquely inwardly throughoutthe height of said face through said of equal width in said portions,each face having continuous equallyspaced thread forming groove meanseach of substantially,- uniform width throughout its length andterminating in sharp intaglio ridge means extending obliquelyinwardheight throughout said shank lo said pointed portion andterminating in a downwardly tapering diametric cutting edge at the tipthereof.

4. Apparatus for use shank and pointed portions, of substantially equaldepth in said shank -portion and of progressively decreasing depth insaid pointed portion.

6. A pair of relatively movable one piece screw j thread rolling dieshaving opposing surfacesadapted to contact each other in use, eachhaving a face comprising a continuous cavity having a lowerwall inclinedslightly upwardly from' front to rear having a cgdperating substantiallyflat shank forming port on and a point forming por'- rtion taperingoutwardly tothe surface oi said die beyond said cavity, eaclf facehaving continnous thread forming groovexmeans each of substantiallyuniform width throughout its length and terminating in a sharp intaglioridge extending obliquely inwardly thereof at substantially equallyspaced distances throughout the height of said face through said shank'and pointed portions, of substantially equal depth in said shankportion and of progressively decreasing Idepth in said pointed portion.

7. A one piece screw thread rolling die having a face comprising acontinuous cavity having a in rolling threads on a lower wall inclinedslightly upwardly from front of the corl progressively at substantiallyequally spaced distances to rear having a cooperating substantially flatshank forming portion and a point forming portion tapering outwardly tothe surface of said die beyond said cavity, said face having contin-Iuous equally spaced thread forming groove means each of substantiallyuniform width throughout its length and terminating in a sharp intaglioridge extending obliquely inwardly 4thereof at substantially equallyspaced distances throughout the height of said face through said shankand .rpointed portions, of substantially equal depth in said shank-portion and of progressively decreasing depth in said pointed portion.t

8. Acne piece screw thread rolling die having a. face comprising acontinuous cavity having a 15' lower wall inclined slightly upwardlyfrom front to rear having a cooperating substantially fiat shank formingportion and a point forming portion tapering outwardly to the surface ofsaid die beyond said cavity, said face having continuous lthread.forming groove means each of substantially uniform width throughout itslength and terminating in a sharp intaglio ridge extending obliquelyinwardly thereof at substantially equally spaced distances throughoutthe height of said face through said shank and pointed portions, ofsubstantially equal depth in said shank portion and of progressivelydecreasing depth in said Apointed portion.

WILLIAM A. DEVELLIER.

